Potentiometers



POTENT IOMETERS Filed Jan. 50, 1969 --2 sheets-shear United States Patent 3,537,055 POTENTIOMETERS Roger A. Simon, Crawley, Reginald Hoad, Shoreham-by- Sea, and David S. Terrett, Burgess Hill, England, assignors to Electronics Associates, Inc., Long Branch, NJ., a corporation of New Jersey Filed Jan. 30, 1969, Ser. No. 795,241 Claims priority, application Great Britain, Jan. 30, 1968, 4,765/ 68 Int. Cl. H01c /00 US. Cl. 338-149 7 Claims ABSTRACT OF THE DISCLOSURE The invention resides in potentiometers having helical resistance wire and a wiper mounted on a nut which itself is mounted on a threaded shaft whereby, upon rotation of the nut on the shaft, the wiper moves along the resistance element. The connection of the wiper to a terminal on the potentiometer housing is via a conductive bar which is used for driving the nut, the bar being slidably engaged with the nut and being fixed at an eccentric position to a rotatable driving member.

Additionally a novel stop arrangement is provided in which a projection on the nut transversely engages an abutment whereby the angular disposition of the abutment defines the limit of movement of the nut.

This invention relates to potentiometers.

Potentiometers have already been proposed in which the resistance wire is in the form of a helix mounted in a housing and in which the wiper is carried on a nut which is located inside the helix and is itself carried on a threaded shaft, of which the pitch of the threads is the same as the pitch of the helix. The potentiometer is operated by rotating the nut so that the wiper moves along the resistance element. The connection of the wiper to a terminal fixed on the housing has been by way of a flexible lead. This lead is subjected to a considerable amount of bending as the wiper is moved back and forth and is therefore liable to break.

An object of the invention is to provide an improved potentiometer in which the requirement for such a lead is avoided.

A further object of the invention is to provide a potentiometer having novel and accurate stop means defining the limit of movement of the wiper.

Embodiments of a multi-turn potentiometer are described below with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of a first embodiment,

FIG. 2 is an end view of the embodiment shown in FIG. 1,

FIG. 3 is a perspective view of parts of the embodiment shown in FIG. 1,

FIG. 4 is a longitudinal sectional view of a second embodiment, and

FIG. 5 is a sectional view taken on the line V-V of FIG. 4.

The multi-turn potentiometer shown in FIGS. 1 to 3 comprises an outer cylindrical shell 11 which is formed ice internally with a helical groove in which a helical resistance element 12 is secured in position. Two terminal posts 13 and 14, screwed home into respective threaded holes in the shell 11, each incorporate a spring-urged contact 15 which bears against the resistive element 12, so that the terminal posts are in contact with the element 12 at points which, in the illustrated potentiometer, are spaced apart by ten helical turns of the element 12.

At one end of the shell 11 is fitted, and secured by means such as a circlip l6, a closure disc 17 moulded round a central member 18 which it thus locates coaxially with the shell 11 and element 12. The member 18 has an outwardly projecting end 18a threaded to receive a nut (not shown) by means of which the potentiometer, when the end 18ais fitted through an aperture in the panel, can be secured in position on the panel. A part 18b of the member 18 which extends inside the shell 11 is also threaded, with a pitch equal to that of the element 12. Rotation of the disc 17 and member 18 relative to the shell 11 and element 12 is prevented by a pin 19 which passes through the shell 11 and the disc 17 and which crosses, radially, through an annular groove 20 formed on the inside surface of the disc 17. The shell 11 is closed at its other end by a disc 21, similarly provided with an annular groove 22 and held in position by a spring clip 23 and by a pin 24 which crosses the groove 22 radially.

The member 18 has an axial bore in which is rotatably disposed a shaft 25. At its end adjacent the disc 21, the shaft 25 has non-rotatably mounted on it an insulating bush 26 surrounded by a slip ring 27 which is non-rotatable relative to the bush 26 and thus to the shaft 25. A third terminal post 28 of the potentiometer, threadedly mounted on the shell 11, has a pick-up brush in the form of a spring wire 29 which bears against the slip ring 27 (preferably in an annular groove provided in the cylindrical periphery thereof). Axial movement of the shaft 25 relative to the member 18 is prevented by the bush 26 and by a circlip 30 bearing against the end of the member 18 and seated in a groove provided on the shaft 25.

A circular nut 31, carrying a spring wiper contact 32 (see FIG. 3) which rides on the resistance element 12, is threadedly engaged on the threaded portion 18b of the member 18; and rotation of this nut causes the wiper contact 32 to track along the helical element 12. For elfecting this rotation of the nut 31, two rods 33 and 34 are mounted in the slip ring 27 and extend parallel to the potentiometer axis, overlying the part 18b of the member 18; and these rods are received as sliding fits in bores which extend through the nut 31 in the axial direction. The wiper contact 32 has a tail which passes under the rod 33 in sliding contact therewith and thus in electrical connection with the terminal post 28 via the slip ring 27 and brush 29. The nut 31 also carries (see FIG. 3) a pin 35 which projects from it in both axial directions. The slip ring 27 has a bore 36 in register with the pin 35, one end of which passes completely through the slip ring 27 as the nut 31 is screwed towards the slip ring by rotating the shaft 25. The pin 35 co-operates with the pins 19 and 24 to provide positive stops limiting rotation of the shaft 25. As the nut 31 is moved axially towards one end of the part 18b of the member 18, the corresponding end of the pin 35, during some particular rotation of the shaft 25, begins to enter the groove 20 or 22 and just grazes the pin 19 or 24. One further rotational turn of the shaft'25 brings the pin 35 once again to the pin 19 or 24, but this time more deeply in the groove 20 or 22 so that it positively abuts against the pin 19 or 24 and further misses or rotation of the shaft 25 and nut 31 in the same direction is prevented. By suitable angular positioning of the pins 19 and 24, taking account of the effective angular position of the contact between the wiper 32 and the element 12, it may be arranged that the pins 19 and 2 4 stop further move ment of the nut 31 when the wiper 32 is in contact with the same points of the element 12 as the two contacts 15, respectively. These two points may, as illustrated, be ten helical turns of the element 12 apart.

The second embodiment of the invention, shown in FIGS. 4 and 5, also comprises a shell 11, a helically wound resistance element 12 wound therein, terminal posts 13 and 14 (not visible in FIGS. 4 and 5) in electrical connection with the element 12, a closure disc 17 secured in place by means (not shown) and having rigidly secured axially thereof a central member 18 with an out wardly projecting threaded end 18a and a part 18b threaded externally with the same pitch as the element 12, a second closure disc 21 secured in place by a spring clip 23, and a shaft 25 which, in the embodiment shown in FIGS. 4 and 5, is rotatably mounted within the member 18 by a ball bearing 41 and a bearing bush 42. One end of the shaft 25, projecting beyond the bearing 41, has an insulating bush 26 fitted to it as a tight push fit, and rotation of the bush 26 relative to the shaft 25 is positively prevented by a pin 43 extending transversely through the shaft 25 and having its projecting ends engaged in slots 44 provided in the bush 26. The bush 26 is embraced by a slip ring 27 which is non-rotatable relative thereto, and the ring 27 has a peripheral groove 27 in which rides a wire contact brush 29 secured to a terminal post corresponding to the post 28 in FIGS. 1 to 3 but not shown in FIGS. 4 and 5. Threadedly engaged on the part 18b of the member 18 is a nut 31 which, as in the embodiment shown in FIGS. 1 to 3, carries a wiper 32 which engages the element 12 and is also in sliding contact with a rod 33- projecting from the slip ring 27; the wiper 32 and rod 33 are, however, not visible in FIG. 4, nor is a further rod 34 with which the slip ring 27 may be provided.

As described thus far, the embodiment shown in FIGS. 4 and 5 is substantially like that shown in FIGS. 1 and 3, and rotation of the shaft 25 occasions, in the same manner, a helical tracking movement of the wiper 32 along the helical resistance element 12. In the embodiment shown in FIGS. 4 and 5, however, somewhat different means are provided for limiting the rotational movement of the shaft 25.

The shaft 25 has a threaded portion 45 on which is threadedly engaged a nut 46. The nut 46 has a longitudinal slot 47 in which is slidingly engaged a pin 48 mounted in the portion 18b of the member 18 and projecting radially inwardly thereof. Thus, the nut 46 cannot rotate, but on rotation of the shaft 25, is moved in the longitudinal direction. The nut 46 is bored longitudinally to receive a tightly fitting pin whose ends 49 and 50 project at opposite ends of the nut 46, and the shaft 25 is provided with two radially projecting pins 51 and 52. Assuming the portion 45 of the shaft 25 is threaded right-handedly, clockwise rotation of the shaft 25 (as viewed from the left in FIG. 4) moves the nut 46 to the left until the pin end 50 is engaged by the pin 52 and further clockwise rotation of the shaft 25 is prevented. This occurs one turn after the pin 52 has just missed or grazed past the leftwardly advancing pin end 50 without, however, being engaged thereby. Similarly, anticlockwise rotation of the shaft 25 is limited by engagement of the pin 51 against the pin end 49; and the pins 51 and 52 may be so positioned as to permit, say, ten turns of the shaft 25 between the two limit positions.

If the part 18b of the member 18 is also right-handedly threaded, a given rotational direction of the shaft 25 produces axial movement of the two nuts in opposite directions; but it will be appreciated that the threaded portions 18b and 45 may be threaded either to the same hand or oppositely. Equally, it will be understood that the pitches of the two threads may be equal or different (though the pitches of the portion 18b and of the helical element 12 are, of course, equal).

What we claim is:

1. A potentiometer comprising a housing,

a helical resistance element mounted in the housing,

a shaft mounted in the housing coaxially of the resistance element and extending therethrough,

external threads formed on said shaft, said threads and said helical resistance element having the same pitch,

a nut threaded on said shaft,

21 wiper carried on said nut and in contact with said resistance element,

a rotatable driving member mounted in the housing coaxially with the shaft,

a conductive drive rod mounted on said drive member at an eccentric position and projecting through the helical resistance element, said drive rod being slidably engaged with said nut whereby rotation of the driving member is transmitted to the nut,

a sliding contact on said nut and in engagement with said drive rod, said contact being electrically connected to said wiper,

and a terminal mounted on said housing and electrically connected to said drive rod, whereby said wiper and said terminal are electrically interconnected.

2. A potentiometer according to claim 1, wherein said sliding contact comprises an end portion of said wiper.

3. A potentiometer according to claim 1, comprising a slip ring mounted on said driving member and a pick up brush mounted on the housing and in electrical contact with said slip ring, said brush being electrically connected to said terminal.

4. A potentiometer according to claim 1, wherein said shaft is hollow and comprising a drive spindle extending coaxially through said hollow shaft, said drive member being fixed on said drive spindle.

5. A potentiometer comprising a housing,

a helical resistance element mounted in said housing,

a shaft mounted in said housing coaxially of said resistance element and extending therethrough,

external threads formed on said shaft, said threads and said helical resistance element having the same pitch,

a nut mounted on said shaft,

a wiper mounted on said nut and engaging said helical resistance element,

drive means for rotating said nut relative to said shaft to cause said wiper to move along said helical resistance element,

a conductive drive rod mounted on said drive means at an eccentric position and projecting through the helical resistance element, said drive rod being slidably engaged with said nut whereby rotation of the drive means is transmitted to the nut,

a sliding contact on said nut and in engagement with said drive rod, said contact being electrically connected to said wiper,

a terminal mounted on said housing and electrically connected to said drive rod, whereby said wiper and said terminal are electrically interconnected,

and stop means defining the limit of movement of said nut, said stop means comprising,

an axial projection carried by said nut at an eccentric position,

and an abutment carried by said housing and positioned to be engaged transversely by said projection whereby the angnlar location of said abutment determines the limit of movement of said nut.

6. A potentiometer according to claim 5, wherein said housing comprises a closure member formed with an axially directed annular groove, said groove being ar- 3,156,888 11/ 1964 Blanco 338-143 X ranged to receive said projection and said abutment being 3,365,690 1/ 1968 Pretot 338-143 disposed in said groove.

7. A potentiometer according to claim 6, wherein said FOREIGN PATENTS abutment comprises a radially disposed pin.

References Cited UNITED STATES PATENTS LEWIS H. MYERS, Primary Examlner 2,871,326 1/ 1959 Weidenman et a1. 338148 D. A. TONE, Assistant Examiner 2,900,614 8/1959 Gach et a1. 338149 10 5 687,270 5/1964 Canada. 

